Sensitivity of different life stages of Indian meal moth Plodia interpunctella to gaseous chlorine dioxide

Gaseous chlorine dioxide (ClO₂), a possible alternative to the fumigant methyl bromide, is a strong disinfecting agent that has strong oxidizing properties and penetration ability. The Indian meal moth, Plodia interpunctella, is one of the most important insect pests of stored food, but its sensitivity to gaseous ClO₂ at different life stages has not yet been studied. We exposed all the life stages of P. interpunctella (i.e., eggs, larvae, pupae, and adults) to ClO₂ at different concentrations for different time periods. The results showed that 100 ppm and 200 ppm ClO₂ for 48 h and 24 h, respectively, resulted in 100% mortality of all P. interpunctella life stages. The order of sensitivity of P. interpunctella to gaseous ClO₂ was: egg > larva > pupa at 50 ppm and 100 ppm, and egg > pupa > larva at 200 ppm. The gas treatment affects the subsequent life stage of P. interpunctella: the gas-treated larvae fail to pupate or emerge as adults. These results suggest that gaseous ClO₂ is a possible alternative to methyl bromide, and it can effectively control all stages of P. interpunctella.     

Analysis of the spatial distribution and dispersion of Plodia interpunctella (Lepidoptera: Pyralidae) in South Korea

This study proposes a novel method to predict the spatial dispersion of Plodia interpunctella by considering the climatic conditions and location of agricultural storage facilities. To accomplish the study objectives, a rearing experiment was conducted, and the CLIMEX model was used to evaluate the climatic suitability of P. interpunctella based on the model parameters estimated from the direct rearing experimental results, in addition to the previous rearing data. Subsequently, we evaluated the distances between the agricultural storage facilities [represented by rice processing complexes (RPCs) and agricultural product processing centers (APCs)] and main ports of grain entry by calculating the flight distance of P. interpunctella. As a result, the climate of South Korea was found unsuitable for P. interpunctella, but the suitability increased throughout the country when considering the indoor temperatures of storage facilities. The analysis of its dispersion with the consideration of grain entry ports, RPCs, and APCs showed that P. interpunctella could be dispersed to areas near storage facilities within 10 d by flying after its first introduction into the ports, as estimated by the calculated flight distance of 32.5 km. However, its dispersion could be accelerated by grain delivery and reach the farthest point in a day. This study provides a methodology to combine species distribution modeling with geographic information system, besides providing a possible scenario of P. interpunctella dispersion, which could serve as the fundamental data for establishing an adequate control strategy.     

End-use quality characteristics of hermetically stored paddy

Four paddy varieties (Bg 352, Bg 300, Bg 358 and Bg 360) were stored in hermetic IRRI bags and common woven polyethylene bags (polybags) at room temperature either uninfested or infested with rice weevils (Sitophilus oryzae (L.)). After 9 months of storage, samples were tested for insect mortality, gas contents, moisture content (m.c.), thousand grain mass (TGM), porosity, hardness, whiteness, total milled rice yield (TMR), head rice yield (HRY), gelatinization temperature, amylose (AC), crude protein (CP), crude fat, free fatty acid (FFA), thiamine and niacin contents and sensory characteristics. These properties after storage were compared with their initial condition. The oxygen content dropped from 21% to 7% and 13.8% for infested and uninfested IRRI bag samples, respectively. The results showed that m.c., of the IRRI bag samples increased significantly (P < 0.05) by 5% when compared to the initial sample but it increased by 15% in polybag stored samples. After 9 months, dry matter loss (DM) was 65% higher in polybag than IRRI bag samples. Highest DM loss was observed in Bg 300 and the lowest DM loss was observed in Bg 358 and Bg 360. Paddy samples stored in IRRI bags showed reduced whiteness compared to polybag stored samples. Storage in IRRI bags significantly increased (P < 0.05) TMR, HRY, AC and sensory values compared to polybag samples. However, paddy samples stored in polybags significantly increased (P < 0.05) their CP and FFA contents while decreasing sensory values, thiamine and niacin contents. The FFA value of polybag samples was 2.5 times higher than IRRI bag samples. Hermetic storage of dry paddy improved overall paddy quality but different end-use quality parameters were observed in the two paddy grain types of short round (Bg 352 and Bg 300) or intermediate bold (Bg 358 and Bg 360).     

Susceptibility of stored product insects to high concentrations of ozone at different exposure intervals

Ozone is a highly reactive gas with insecticidal activity. Past studies have indicated that ozone technology has potential as a management tool to control insect pests in bulk grain storage facilities. The objective of this study was to determine the efficacy of short periods of exposure to high ozone concentrations to kill all life stages of red flour beetle (Tribolium castaneum (Herbst)) (Coleoptera: Tenebrionidae), and Indianmeal moth (Plodia interpunctella (Hübner)) (Lepidoptera: Pyralidae), adult maize weevil (Sitophilus zeamais (Motsch.)) (Coleoptera: Curculionidae) and adult rice weevil (S. oryzae (L)) (Coleoptera: Curculionidae). Insects were treated with six ozone concentrations between 50 and 1800 ppm. The specific objective was to determine minimal time needed to attain 100% mortality. The most ozone-tolerant stages of T. castaneum were pupae and eggs, which required a treatment of 180 min at 1800 ppm ozone to reach 100% mortality. Eggs of P. interpunctella also required 180 min at 1800 ppm ozone to reach 100% mortality. Ozone treatments of 1800 ppm for 120 min and 1800 ppm for 60 min were required to kill all adult S. zeamais and adult S. oryzae, respectively. The results indicate that high ozone concentrations reduce the treatment times significantly over previously described results. Our results also provide new baseline information about insect tolerance to ozone treatment.     

Efficacy of phosphine and insect penetration ability in ZeroFly® bags

The deltamethrin incorporated woven polypropylene ZeroFly® storage bag is a promising novel technology for grain storage. However, if grain stored in ZeroFly bags gets infested and has to be fumigated using phosphine (PH₃), data on the effectiveness of such treatments are needed. Additionally, obtaining field data on ability of stored-product insect pests to breach ZeroFly bags would facilitate insect management. Therefore, efficacy of PH₃ in immature and adult Sitophilus zeamais (Motschulsky), Prostephanus truncatus (Horn), Rhyzopertha dominica (F.) and Tribolium castaneum (Herbst) in experimental cages in maize stored in 100-kg polypropylene (PP), jute and ZeroFly bags was investigated. Post-fumigation mortality of adults was recorded after 7 d, and after 7 wk for immatures. The ability of either S. zeamais or P. truncatus to penetrate fabric of PP, jute and ZeroFly bags was assessed. Phosphine efficacy was good in all the three types of bags and resulted in complete mortality of adults and immatures of the four species tested. Sitophilus zeamais and P. truncatus were more successful in penetrating the PP bag fabric and on average made 84 and 780 holes per bag over a 4 mo-period, respectively; this was followed by jute with 37 and 614 holes. The ZeroFly bag was harder to breach and ≤3 holes per bag were made for both species. This study shows that PH₃ is highly efficacious in insects that infest maize stored in ZeroFly bags, and that these bags are not easily penetrated by stored product insect pests. Hitherto, ZeroFly bags are a good technology for storing grain that is not infested, and fumigation using PH₃ can be effectively conducted if infestation occurs. Therefore, ZeroFly bags can be incorporated in integrated stored product insect management (IPM) programs for bagged grains.     

Spinosad: A new natural product for stored grain protection

Spinosad is a reduced-risk insecticide derived by fermentation from the soil actinomycete, Saccharopolyspora spinosa Mertz & Yao. Spinosad is currently registered in several countries as a grain protectant at a maximum labeled use rate of 1 ppm (1 mg a.i./kg of grain) and with the Maximum Residue Level (MRL) or tolerance on grains set at 1 or 1.5 ppm. Global launch of spinosad as a grain protectant is expected in the near future, pending final acceptance of international residue tolerances for spinosad by major grain importing and exporting countries. Spinosad effectively controls economically important beetle and moth pests associated with stored grain and is also effective against certain psocid species. Spinosad provides grain protection through control of adult and/or immature life stages of pest insects. The pest spectrum of spinosad under commercial grain storage conditions is still being defined, but it is clear from available laboratory and field evaluations on various grains that the lesser grain borer, Rhyzopertha dominica (F.); larger grain borer, Prostephanus truncatus (Horn); rusty grain beetle, Cryptolestes ferrugineus (Stephens); flat grain beetle, Cryptolestes pusillus (Schönherr); red flour beetle, Tribolium castaneum (Herbst); confused flour beetle, Tribolium confusum Jacquelin du Val; Indian meal moth, Plodia interpunctella (Hübner); rice moth, Corcyra cephalonica (Stainton); Angoumois grain moth, Sitotroga cerealella (Olivier); almond moth, Cadra cautella Walker; and the psocid species Lepinotus reticulatus Enderlein and Liposcelis entomophila (Enderlein) are susceptible to spinosad and complete control is to be expected. Other pest species such as the maize weevil, Sitophilus zeamais Motchulsky; rice weevil, Sitophilus oryzae (L.); and sawtoothed grain beetle, Oryzaephilus surinamensis (L.) are susceptible to spinosad to varying degrees, but their overall level of control remains to be verified under commercial grain storage conditions. Spinosad residues are highly stable on grains stored in bins, with a length of protection ranging from 6 months to 2 years. Numerous factors have been shown to impact the overall performance of spinosad, including insect pest species, pest life stage, grain type, grain variety, and formulation type. Spinosad possesses a unique mode of action in insects and controls insect strains resistant to other grain protectants. When launched globally, spinosad will represent a valuable new addition to the limited arsenal of grain protectants and can positively impact global food security. Its combination of high efficacy, broad insect pest spectrum, low mammalian toxicity, and sound environmental profile is unique among existing products currently used for stored-grain protection.     

Susceptibility of different life stages of Indian meal moth Plodia interpunctella (Hübner) and almond moth Ephestia cautella (Walker) (Lepidoptera: Pyralidae) to modified atmospheres enriched with carbon dioxide

The susceptibility of the different life stages of the Indian meal moth Plodia interpunctella and almond moth Ephestia (Cadra) cautella to different modified atmospheres (MAs) containing various concentrations of carbon dioxide (CO₂) was studied as an alternative to methyl bromide fumigation at 27 °C and 60 ± 5% relative humidity (r.h.). The MAs tested were 40%, 60% and 80% CO₂ in air at different exposure times. Results showed that five days were adequate to kill all eggs and pupae of the two moths under all tested MAs. Exposure time needed to be extended to 6 and 7 days at 80% CO₂ to obtain complete mortality of larva of E. cautella and P. interpunctella, respectively. The order of sensitivity of P. interpunctella to MAs was: egg = pupa > larva, while for E. cautella it was: pupa > egg > larva. Generally, eggs and pupae of P. interpunctella were more sensitive to MAs than those of E. cautella but the larvae of the latter were more sensitive.     

The use of modified atmospheres to control Sitophilus zeamais and Sitophilus oryzae on stored rice in Portugal

This study reports the efficacy of using CO₂ against Sitophilus zeamais and Sitophilus oryzae as an alternative treatment to fumigation for rice stored in a rice mill in Portugal. The trials were conducted in a silo containing 40 tonnes of polished rice and in four hermetic big bags of 1 tonne capacity; two with paddy and two with polished rice. The composition of the atmosphere ranged from 90 to 95% CO₂ and 0.7–2.1% O₂. Three trials were carried out at different temperatures and treatment times; stored rice in the silo at 29.6 ± 0.1 °C for 26 days (first trial), at 34.1 ± 0.2 °C for 10 days (second trial), and in big bags at 22 °C for 26 days (third trial).To evaluate the efficacy of each treatment, metal cages with 16 g of infested rice where placed at bottom, middle, top and surface of the polished rice in the silo. Four replications of each type of infested rice containing one-week-old S. zeamais adults, or eggs of S. zeamais or S. oryzae, were incubated in the laboratory, at the same temperature as in the silo, to serve as a control.In all modified atmosphere treatments adults of S. zeamais, and eggs of both S. oryzae and S. zeamais, showed mortality close to 100% and no F1 emergence was recorded in any treatment sample. This was the first time that a Portuguese rice mill used modified atmospheres.     

Spatial analysis of changes in Plodia interpunctella (Lepidoptera: Pyralidae) distribution depending on diets

Plodia interpunctella is a globally important insect pest that infests stored food products. Infestation may cause a substantial increase in economic costs for pest control and entails quality loss and dissatisfaction of consumers. The aim of this study was to predict the potential distribution of P. interpunctella feeding on four different diets (rice bran, vegetables, wheat bran, or walnuts) using a CLIMEX model and provide basic data for the storage and management of processed food products. To estimate the CLIMEX parameter of P. interpunctella feeding on rice bran, the developmental rate at different temperatures was tested, resulting in a lower developmental threshold and the degree days of 12.5 °C and 461 DD, respectively. In the spatial analysis, the climatic suitability of P. interpunctella feeding on rice bran was the highest when compared to other diets and particularly higher than that of walnuts in 23.3% of the total area. Our results are expected to provide basic data for the management of P. interpunctella based on species distribution modeling, which, in our study, produced different predicted distribution patterns based on diet and climate.     

Laboratory studies on parasitism of Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae) by two species of Trichogramma Westwood (Hymenoptera: Trichogrammatidae) in different grains,and evaluation of traps for their monitoring

The aim of the present study was to evaluate two species of egg parasitoids under laboratory conditions for biological control of the Indian meal moth Plodia interpunctella, an emerging stored product pest in bulk grain. Trichogramma evanescens proved to be a better candidate for biological control compared to T. cacoeciae as it accepted and parasitised a higher percentage of Indian meal moth eggs. Consequently the foraging of T. evanescens was studied in detail. Preferred oviposition sites on individual seeds by P. interpunctella are the germ region and the raphe. Moth eggs were parasitised at both regions. P. interpunctella eggs received higher parasitism at the germ region compared to the raphe. In stored grain and rice, P. interpunctella eggs can be found in the upper 8 cm of the bulk. Foraging parasitoids were shown to enter up to this depth into wheat, oats, and paella and Basmati rice. Wheat and oats were found most suitable for foraging, as larger numbers of T. evanescens were able to reach this depth as compared to the rice varieties. Among different traps, i.e. probe traps, cone traps and wiregauze tubes with adhesive cardboard, cone traps proved best for monitoring T. evanescens. These cone traps as well as the wiregauze tubes were used for the first time to monitor Trichogramma spp. in bulk grain. Cone traps recorded T. evanescens both when placed on the grain surface and in 5 cm depth within the grain irrespective of the release technique of Trichogramma, i.e. release from cardboard cards or sprinkling loose parasitised eggs. The potential for release of Trichogramma spp. within an integrated control strategy for the Indian meal moth in bulk stored grain and rice is discussed.     

Pest control treatments with phosphine and controlled atmospheres in silo bags with different airtightness conditions

The silo bag technology has been extensively used in Argentina for storing grains (e.g. wheat, corn, barley, sunflower and soybean among others) since the mid-1990s. Silo bag are widely considered a hermetic storage system in which PH₃ fumigation is frequently implemented for pest control. However, there is insufficient information regarding the potential airtightness of silo bags and how it could affect the performance of fumigation and controlled atmosphere treatments. In this study, a pressure decay test (PDT) was implemented to characterize airtightness level of silo bags set up following various procedures. PH₃ fumigation treatments with different dosages and hermeticity levels were conducted, and fumigant concentration was monitored. Controlled atmosphere treatments with carbon dioxide were also implemented in silo bags with different hermeticity levels. Results showed that less than half of the bags tested in the field had a PDT indicated for fumigation (90 s), and that when a bag without thermo sealing was used for fumigation, this treatment failed. However, it was demonstrated that with simple and inexpensive practices silo bags can achieve high enough airtightness conditions to implement successful PH₃ fumigation (5 days above 200 ppm with a dosage of 1 g of PH₃/m³) and even controlled atmosphere treatments (more than 18 days with CO₂ concentration above 70%). This study shows that silo bags could be used as a cost competitive hermetic storage technology for performing controlled atmosphere treatments.     

Efficacy of methoprene for multi-year protection of stored wheat,brown rice,rough rice and corn

Hard red winter wheat, brown rice, rough rice, and corn were treated with the insect growth regulator (IGR) methoprene at rates of 1.25 and 2.5 ppm, held for 24 months at ambient conditions in buckets on the floor of a grain bin, and sampled every two months. Bioassays were done by exposing 10 mixed-sex adults of Rhyzopertha dominica (F.), the lesser grain borer, and Tribolium castaneum (Herbst), the red flour beetle, on wheat, R. dominica and Sitotroga cerealella (Oliver), the Angoumois grain moth, on brown rice and rough rice, and T. castaneum and S. cerealella on corn. Sample size for all commodities was about 80 g, and these samples were held for 3 months at 27°C-60% r.h. Both rates of the IGR completely suppressed adult progeny development of R. dominica with little resulting feeding damage, sample weight loss, or insect damaged kernels (IDK). Some adult progeny production of S. cerealella and resulting IDK occurred at both rates on rough rice, brown rice, and corn, but was far less than in untreated controls. There was little adult progeny production but some feeding damage caused by larval T. castaneum in the treated wheat and corn but again far less than in untreated control. Allowing continual exposure of parental adults on grains treated with an IGR, rather than exposing those parental adults for a short time period, may give more accurate evaluations of residual efficacy. Results show that methoprene used as a grain protectant will give residual control of stored product beetles for 24 months, but complete control of S. cerealella may require inclusion of a contact insecticide.     

Evaluations of the new deltamethrin-treated all-in-one hermetic bag for the control of the Khapra beetle,Trogoderma granarium (Everts)

The khapra beetle, Trogoderma granarium (Everts), is a highly destructive stored product insect that presents a significant threat to stored bagged grain. Hermetic packaging is designed to maintain the quality and safety of stored grain, while continually protecting the grain from insect infestations during storage. The objective of this research was to evaluate a prototype deltamethrin, all-in-one treated hermetic bag on contact efficacy, larval mobility, and the control of T. granarium in artificially infested wheat. The insecticidal activity of the deltamethrin-treated packaging was tested against larvae and adults of T. granarium through contact bioassays. There was a significant reduction in responsive adults after 5 day and >86% of larvae were unresponsive after 9 d of exposure on the treated bag. Trogoderma granarium movement toward a food bait was <10% after a 24 h exposure on the treated bag compared to ~45% of larvae on untreated bag. Lots of 15 kg of wheat were artificially infested with 100 T. granarium larvae and placed inside treated and untreated storage bags, sealed, and stored in a semi-field warehouse, and observed after 2, 6, and 8-weeks for T. granarium survival and grain quality attributes. The weight and number of insect damaged kernels was lower across all storage intervals for grain held in the treated bags, as compared with control bags. Live adult T. granarium were observed at 2-weeks in treated and untreated bags, but there were no live adults observed after 8-weeks of storage in both bags. The new prototype hermetic bags maintained positive grain qualities, however more information on the hermetic parameters are needed to understand how some individuals survived.     

A study on the feasibility of quantifying the population density of stored product insects in air-tight grain storage using CO2 concentration measurements

This study was aimed at estimating the number of insects per 1 kg of paddy (IPK) in an air-tight mock-up silo by CO₂ concentration monitoring. The first experiment was to determine the respiration rates of adult Sitophilus zeamais, Rhyzopertha dominica, and Tribolium castaneum. CO₂ concentrations were recorded from groups of 50, 100 and 200 insects with and without 125 g of brown rice. The respiration rate was calculated from the slope of the CO₂ concentration curve. A sample size of at least 100 insects was recommended. In 100-insect group, with the presence of food the respiration rates of S. zeamais, R. dominica, and T. castaneum were 9.57–14.13, 1.96–3.93 and 4.59–11.76 μl_CO2/insect−h, respectively. In the second experiment, S. zeamais populations at actual IPK = 2, 0.5, 0.25, 0.125 and 0.0625 in a 1.618 m³ silo filled with paddy were quantitatively determined. Similarly, R. dominica and T. castaneum populations at actual IPK = 0.5, 0.25, 0.125 and 0.0625 in 0.064 m³ silos were estimated in the third experiment. In each trial, small containers filled with a known number of adult insects along with brown rice were buried in the silo. Additionally, a control silo containing only disinfested paddy was set up in parallel. The insect population density was calculated from the difference in the slopes of the CO₂ curves between the infested and control silos divided by the respiration rate of one insect. On average, for each species and each infestation level the estimated population density was not greater than twice of the actual ones. Although several assumptions (e.g., silos being completely sealed, only one species and one life stage of infesting insects) had to be made, monitoring CO₂ concentrations could potentially be an effective tool for determining insect population density during grain storage.     

Cumulative oxygen consumption during development of two postharvest insect pests: Callosobruchus maculatus Fabricius and Plodia interpunctella Hübner

Insect pests such as Callosobruchus maculatus Fabricius and Plodia interpunctella Hübner cause substantial losses to grain during postharvest storage. In the last few years, hermetic storage technologies have been successfully used by smallholder farmers in Africa and Asia to protect their harvested grain against insect pests. Hermetic technologies owe much of their effectiveness to restricting oxygen availability to insects confined in the containers. There is a need to better understand the biology of specific storage insect pests and their responses to hypoxia. We employed a novel and non-invasive analytical technology, the OxySense 5250i, to measure oxygen levels in closed containers, and evaluated its effectiveness in measuring the total oxygen consumption of two insect pests during their development: C. maculatus and P. interpunctella. The total amount of oxygen consumed by C. maculatus during its larval development period determined with the OxySense apparatus was not different from that previously recorded using another instrument, the Mocon Pac Check 325 gas analyzer. Using the OxySense 5250i, we found that P. interpunctella consumes nearly three times as much oxygen per insect over its larval-to-adult developmental period compared to C. maculatus. Information on the lifetime oxygen consumption of insects provides relevant information to the effectiveness and ability of hermetic technologies to protect stored products against insect pests.     

Fumigation toxicity of monoterpenoids to several stored product insects

Twenty naturally occurring monoterpenoids were evaluated in a preliminary fumigation screening test on some important stored-product pest insects, including the rice weevil, Sitophilus oryzae, the red flour beetle, Tribolium castaneum, the sawtoothed grain beetle, Oryzaephilus surinamensis, the house fly, Musca domestica, and the German cockroach, Blattella germanica. Cineole, l-fenchone, and pulegone at 50 μg/ml air caused 100% mortality in all five species tested. Ketone compounds were generally more toxic than other monoterpenoids. Three monoterpenoids, the ketones pulegone, l-fenchone, and the aldehyde perillaldehyde, were selected for further study. They were effective against T. castaneum in the fumigation assay; however the toxicity was relatively low in comparison to dichlorvos. LC₅₀ values of these three monoterpenoids tended to decrease at longer exposure times and higher temperatures. Inclusion of either maize kernels or house fly medium (HFM) increased LC₅₀ values, HFM more so than maize kernels. Monoterpenoids may be suitable as fumigants or vapor-phase insecticides because of their high volatility, fumigation efficacy, and their safety.     

Effect of gaseous chlorine dioxide treatment on the quality of rice and wheat grain

Gaseous chlorine dioxide (ClO₂), which is a strong disinfecting agent with strong oxidation properties and penetration ability, is used to control insect pests and fungal contamination in stored grains. However, the effect of gaseous ClO₂ on stored grain has yet to be reported. In the present study, we exposed rice and wheat seeds to several concentrations of ClO₂ gas for various durations and found that the viability of rice was affected less than that of wheat. After 100 ppm of gaseous ClO₂ for 12 h, the normal rice seedling rate was not significantly different than that of the control. However, that of wheat was significantly decreased. We also measured the ClO₂ residueon stored rice and wheat after 200 ppm of gas treatment for 24 h. After 10 days of storage following the treatment, ClO₂ and chlorine were not detected on either rice or wheat. Chlorite was detected on rice at 0.22 mg/kg of grain; however, it was not detected on wheat. These results suggest that gaseous ClO₂ treatment affects the viability of rice and wheat seed but leaves minimal chemical residue.     

Performance of triple bagging hermetic technology for postharvest storage of cowpea grain in Niger

Triple bagging technology for protecting postharvest cowpea grain from losses to the bruchid, Callosobruchus maculatus Fabricius (Coleoptera: Chrysomelidae: Bruchinae) is currently being adopted on a fairly large scale in ten West and Central African countries, including Niger. The triple bag consists of two inner high-density polyethylene bags acting as oxygen barriers, which in turn are encased in an outer woven polypropylene bag that serves primarily for mechanical strength. These hermetic bags, available in either 50 or 100 kg capacity, are called Purdue Improved Cowpea Storage (PICS) bags. Adoption of PICS technology in West and Central Africa has been driven by its effectiveness, simplicity, low cost, durability, and manufacture within the region. From surveys on adoption we discovered that farmers have begun to re-use bags they had used the previous year or even the previous two years. In the present study, we compared the performance of three different types of PICS bags: (1) new 50 kg (2) new 100 kg bags and (3) once-used 50 kg bags, all filled with naturally infested untreated cowpeas. In these PICS bags the O₂ levels within the bags initially fell to about 3 percent (v/v) while the CO₂ rose to nearly 5 percent (v/v). After five months of storage, new and used 50 kg bags and new 100 kg bags preserved the grain equally well. There were greatly reduced numbers of adults and larvae in the PICS bags versus the controls, which consisted of grain stored in single layer woven bags. The proportion of grain having C. maculatus emergence holes after five months of storage in PICS bags was little changed from that found when the grain was first put into the bags. The PICS technology is practical and useful in Sahelian conditions and can contribute to improved farmers' incomes as well as increase availability of high quality, insecticide-free cowpea grain as food.     

A simple instrument-free gaseous chlorine dioxide method for microbial decontamination of potatoes during storage

An instrument-free gaseous chlorine dioxide (ClO₂) method to control microorganisms on potatoes during storage was developed. Gaseous ClO₂ was generated by combining an equal amount of impregnated sodium chlorite and activating acids in a sachet without using any solution or equipment. After activation by mixing, the sachet was placed in the application area. The decontamination efficiency of ClO₂ on natural microbiota including total microorganisms, yeasts and molds, and inoculated Pseudomonas aeruginosa on potatoes was investigated. Different treatments using 2, 3, and 4 g of materials and various time intervals (2.5 and 5 h) to generate 16, 20, 24, 30, 32, and 40 mg/L of ClO₂ were evaluated. The results were effective for natural microbiota, showing over a 5 log CFU/potato reduction with a 4 g treatment after 5 h. For P. aeruginosa, there was almost a 6 log CFU/potato reduction after 5 h of the 4 g treatment. The lowest treatment tested (2 g at 2.5 h) showed reductions of 1.7, 1.9, and 2.3 log CFU/potato for total microorganisms, yeasts and molds, and P. aeruginosa, respectively. Gaseous ClO₂ did not affect the overall visual quality of the potato. The residue of ClO₂ decreased to <1 mg/L after 14 days for each treatment, indicating ClO₂ dissipates naturally over time.     

Phosphine fumigation of silo bags

Fumigation with phosphine has the potential to disinfest grain stored in silo bags but only limited research has been conducted on whether phosphine fumigation can be undertaken effectively and safely in this form of storage. Fumigation with phosphine was tested on two (70 m) replicate silo bags each containing 240 t of wheat (9.9 and 9.2% m.c.). The target application rate of phosphine was 1.5 g m⁻³ with a fumigation period of 17 days. Aluminium phosphide tablets were inserted into each bag at ten release points spaced at 7 m intervals starting 3.5 m from either end of the bag. A total of 14 bioassay cages containing mixed age populations of strongly phosphine resistant Rhyzopertha dominica (F.) were inserted into each fumigated silo bag. Complete control of all life stages of R. dominica was achieved at all locations in the fumigated silo bags. Phosphine concentrations at release points increased rapidly and remained high for the duration of the fumigation. Concentrations at midway points were always lower than at the release points but exceeded 215 ppm for ten days. The diffusion coefficient of available phosphine averaged over the first three full days of the fumigation for both fumigated silo bags was 2.8 × 10⁻⁷. Venting the silo bag with an aeration fan reduced the phosphine concentration by 99% after 12 h. Relatively small amounts of phosphine continued to desorb after the venting period. Although grain temperature at the core of the silo bags remained stable at 29 °C for 17 days, grain at the surface of the silo bags fluctuated daily with a mean of 29 °C. The results demonstrate that silo bags can be fumigated with phosphine for complete control of infestations of strongly phosphine resistant R. dominica and potentially other species.